String instrument bridges have six functions to perform which are of equal importance in the overall level of quality of an instrument. These functions include the following:
1) To transfer as close to 100% as possible the vibrations of the strings to the body of the instrument.
2) To influence the tonal quality of the vibrations in a way that is generally considered aesthetically pleasing or pleasing specifically to the musician playing it.
3) To enhance or aid in the production of vibrations or notes that can be sustained for long periods of time. The term “legato” is commonly used in the directions from the composer on how to perform a piece of music. The dictionary states the meaning of legato as “in a smooth flowing manner, without breaks between notes.” Throughout the ages the majority of instrumental music, no matter what the style or from what period, has been written with the intension of imitating the human voice as it is used to sing. Most string instruments are harmonic instruments. The are able to play music called chords which are notes stacked on top of one another and played at the same time. The music notation is written up and down or vertically, as it may be. When performed, however, it is to be played horizontally, along one or more lines in which the notes are to sound smooth and connected. The challenge to play legato is even more difficult in the case of the string instruments referred to as plectrum instruments, i.e. guitars, basses, banjos, mandolins for the string is plucked. With this plucking action the length of time that the note or vibration sustains is more limited than many other musical instruments so an instrument that sustains well is paramount for the plectrum string instrumental performance.
4) To adjust the string height vertically, described also as close to or away from the instrument. This is for the purpose of providing an adjustment when needed for the clearance of the string(s) from the fretboard or fingerboard located on the neck of the instrument. This string height also is adjusted as per the comfort or ease of play for the musician otherwise known as “the action.”
5) The horizontal movement of the bridge or bridge pieces for the purpose of adjusting the intonation of the instrument. Intonation is the accuracy of pitch on a musical instrument. Various thicknesses in the strings diameter dictate the length of the string and effect the placement of the bridge or bridge pieces upon which the string rests.
6) The musician makes contact with the instrument when touching the strings. To provide a solid and full “feel” and thus feedback of information in to the fingertips, hands and body and mind of the musician the bridge must works equally in concert with the strings and body of the instrument in this function. This creates an environment, which influences the instrumental musicians personal expression of the sound and music.
Stringed instruments, particularly electric and acoustic guitars, typically require a bridge on the body of the instrument to lift the strings so that an appropriate gap exists between the strings and the fretboard or fingerboard of the instrument. Bridges that are utilized on electric guitars are often adjustable in height such that this gap, or “action,” can be set to provide a desired tone and/or feel when the strings are depressed onto the fretboard by the player's fingers. Such bridges typically also provide adjustment of the intonation or position of the bridge or bridge piece(s). Bridges further function to transfer the vibrations of the instrument's string(s) to the body of the instrument, thus causing resonation of the instrument body and increasing resonation of the strings.
The past several decades have seen minimal changes and improvements in the basic design of the bridge. Generally, the height of the string(s) has been adjusted using two approaches. The first is the tune-o-matic type bridge design. In this design the strings rest on an object commonly called a bridge assembly. The bridge assembly rests on two threaded poles or posts, one at each end of the bridge assembly. These poles or posts are mounted into a threaded base. The poles or posts can be raised or lowered by turning their threaded shafts, thus raising or lowering them in much the same manner as screwing a screw into or out of a piece of wood. Turning the threaded shaft to the right causes it to recede down into the threaded base, and turning the threaded shaft to the left causes it to rise up out of the threaded base.
Another version of the tune-o-matic bridge has the threaded poles or posts secured in a fixed position. Each pole or post has a threaded wheel which is free to turn. The bridge assembly sits upon these two wheels. Again a right turning of the wheel raises it up the threaded pole or post, thus causing the bridge assembly to rise with the wheel upon which it sits, and a left turning of the wheel lowers it down the treaded pole or post, thus lowering the bridge assembly along with the wheel.
Another approach to adjusting the height of the strings is used in hard-tail or fixed bridges and tremolo bridges. Both of these bridge designs typically have a bridge plate securely mounted to the instrument body and individual bridge pieces attached to a bridge body upon which the strings rest. These bridge pieces are secured to the bridge plate with an adjustment screw or bolt. The function of that screw or bolt will be described in further detail below. The bridge piece(s) typically have two threaded holes in them. These two threaded holes accept two threaded screws, sometimes called feet. As in the tune-o-matic bridge example described above, turning the threaded screw or feet to the right raises the bridge piece up and turning it to the left lowers the bridge down.
Adjustment of intonation on stringed instruments, particularly electric guitars, is typically performed by adjusting the position of the bridge piece(s) along the axis that is parallel to the strings. In most bridge designs this is done by moving individual bridge piece(s) forwards or backwards by turning a screw or bolt which is attached to the individual bridge piece. The screw or bolt is anchored to the bridge plate through a hole in the rear of the bridge plate. The bridge piece is often held in place with tension between the bridge piece and bridge plate provided by a spring wrapped around the above adjustment screw or bolt. Again the bridge piece has a threaded hole that accepts the threaded screw. As the screw is turned to the right the bridge piece moves down the string length and towards the end of the bridge plate. As the screw is turned to the left the bridge piece moves up the string length and away from the end of the bridge plate.
Transfer of the vibrations of the string to the body of the instrument is accomplished via contact of the string with the bridge or bridge pieces, which then make contact with their poles, posts, or adjustable screws or feet, which in turn make contact with the body of the instrument.
The bridge design, its materials, and amount of contact surface of those materials, are important factors in providing the musician with feedback or “feel” of the instrument. This in turn affects the ability of the musician to communicate his expression and interpretation of music written for the instrument. Prior bridge designs that use adjustment feet and adjustment studs for purposes of raising and lowering strings cause a tremendous loss of vibration transference from string to bridge to instrument body.